Molded product having coating film

ABSTRACT

A process for forming a coating layer on the surface of a molded product by boiling a coating solution in a closed metal mold. The molding process includes depressurizing the cavity of the metal mold, boiling a coating solution in the cavity and injecting a urethane material into the cavity under reduced pressure.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a molded product and a processfor manufacturing a molded product.

[0002] Typically, vehicle steering wheels are manufactured by resinmolding. A core bar is first set in a metal mold at a predeterminedposition. Thereafter, a resin material is injected into the cavity ofthe metal mold and cured. A urethane resin is used as the resinmaterial. A coating film having light resistance is formed on thesurface of the resin molded part to prevent discoloration of theurethane resin by exposure to light.

[0003] A method of forming the coating film includes applying a coatingto the inner wall of the metal mold (the surface of the cavity) prior tomolding. More specifically, a coating solution is sprayed on the innerwall of the opened metal mold with a spray gun. The metal mold is closedand a filler material (urethane material) is injected into the moldcavity and cured. Thus, a molded product having a coating film on thesurface is produced. A molding method in which a predetermined materialis injected into the cavity and cured by a chemical reaction is called“reaction injection molding” (RIM).

[0004] However, when a coating solution is applied with a spray gun, thecoating may be applied to parts other than the surface of the cavity ormay scatter into the air without adhering to the surface of the cavity.Therefore, the adhesion efficiency of the coating is low. Since thecoating applied to surfaces other than the surface of the cavityproduces a burr after molding, the step of removing this burr isrequired. Further, the material that scatters into the air stains thework site.

[0005] On the other hand, when a coating solution is directly applied toa molded product with a spray gun, it is difficult to apply the coatinguniformly. It is particularly difficult to properly apply the coating tothe parting line of a molded product. Therefore, the light resistance ofthe steering wheel may not be complete.

SUMMARY OF THE INVENTION

[0006] It is an object of the present invention to,provide a moldedproduct having excellent light resistance and a manufacturing processfor the same.

[0007] To achieve the above objective, the present invention provide aprocess for manufacturing a molded product having a coating layer on thesurface. The process includes forming a coating layer on the wallsurface of a cavity while a metal mold is closed, and filling a fillermaterial in the cavity.

[0008] Another aspect of the present invention provides a molded productformed by injecting a filler material into the cavity of a metal mold,wherein the filler material is coated with a film having a substantiallyuniform thickness.

[0009] Furher aspect of the present invention provides a steering wheelhaving a first side facing a driver and a second side, which is oppositeto the first side. The steering wheel is coated with a film. The film isthicker on the first side than on the second side.

[0010] Furher aspect of the present invention provides a process formolding a steering wheel providing a metal mold having a mold cavity.The cavity is formed such that a grip portion of the steering wheelfaced downward. The process includes boiling a coating solution, duringwhich a coating layer is formed on the wall surface of the cavity fromthe coating solution, and supplying a predetermined filler material intothe cavity.

[0011] Furher aspect of the present invention provides a process formanufacturing an insert molded product. The process includes setting aninsert member in a metal mold, forming a coating layer on the wallsurface of a cavity in the metal mold while the metal mold is closed,and depositing a filler material into the cavity.

[0012] Furher aspect of the present invention provides an insert moldedproduct formed by molding a filler material. The product includes aninsert member, an intermediate layer formed from the same material asthe coating film and located between the insert member and the fillermaterial, and a coating film formed on the surface of the fillermaterial, the coating film having a substantially uniform thickness.

[0013] Furher aspect of the present invention provides a method ofcoating a coating on the wall surface of a cavity in a metal mold. Themethod includes closing the metal mold, supplying a solution of thecoating into the cavity, and depressurizing the cavity.

[0014] Furher aspect of the present invention provides a method ofcoating a coating on the wall surface of a cavity in a metal mold. Themethod includes closing the metal mold, depressurizing the cavity, andsupplying a coating solution into the cavity during the depressurizingstep.

[0015] Furher aspect of the present invention provides a molded productof a urethane resin formed by foam molding using water. The moldedproduct includes a core portion molded by foaming a urethane material,and a coating film having a substantially uniform thickness, the filmbeing formed on the surface of the core portion, wherein the surfacecharacteristics of the metal mold is transferred to the coating.

[0016] Furher aspect of the present invention provides a process formanufacturing a urethane resin molded product formed by foam moldingusing water. The process includes boiling a coating solution in a cavityin a metal mold while the metal mold is closed, during which time acoating film is formed on the wall surface of the cavity from thecoating solution, and supplying a urethane material into the cavity atnormal pressure.

[0017] Furher aspect of the present invention provides a product moldedwith urethane material in a mold cavity. The product includes a coreportion made of a highly foamed urethane material, a skin layer formedon the outside of the core portion, the skin layer being made of aurethane material that has less foaming than the core portion, and acoating film formed with a substantially uniform thickness on thesurface of the skin layer, wherein the surface characteristics of thecavity are transferred to the film.

[0018] Furher aspect of the present invention provides a process formanufacturing a foamed urethane molded product having a surface skinlayer. The process includes depressurizing a cavity in a metal mold,boiling a coating solution in the cavity, forming a coating layer on thewall surface of the cavity during the boiling step, and injecting aurethane material into the cavity under reduced pressure.

[0019] Furher aspect of the present invention provides a process formanufacturing a resin molded product, wherein molding and coating areperformed simultaneously. The process includes applying a coatingsolution to the wall surface of a cavity in a metal mold, boiling thecoating solution in the cavity under reduced pressure to form a coatinglayer on the wall surface of the cavity, heating a resin material toreduce flow resistance, supplying the heated resin material into thecavity, and curing the resin material in the cavity.

[0020] Furher aspect of the present invention provides a product moldedwith resin material. The flow resistance of the resin material can bereduced by heating. The resin material is coated with a film having asubstantially uniform thickness.

[0021] Furher aspect of the present invention provides a process formanufacturing a urethane molded product. The process includes forming acoating layer on the surface of a cavity of a closed metal mold, firstinjecting a first urethane material containing a pigment into thecavity, and second injecting a second urethane material that includes alarger amount of a pigment than the first urethane material.

[0022] Other aspects and advantages of the present invention will becomeapparent from the following description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The features of the present invention that are believed to benovel are set forth with particularity in the appended claims. Theinvention, together with objects and advantages thereof, may best beunderstood by reference to the following description of the presentlypreferred embodiments together with the accompanying drawings in which:

[0024]FIG. 1, FIG. 2 and FIG. 3 are diagrams illustrating a process formolding a steering wheel according to a first embodiment of the presentinvention;

[0025]FIG. 4 is a perspective view of the steering wheel of the firstembodiment;

[0026]FIG. 5 is a sectional view of the grip portion of the steeringwheel of FIG. 4;

[0027]FIG. 6 is a diagram schematically showing an injection moldingmachine according to a second embodiment of the present invention;

[0028]FIG. 7, FIG. 8, FIG. 9 and FIG. 10 are sectional viewsillustrating a process for molding a steering wheel according to a thirdembodiment of the present invention;

[0029] FIGS. 11 to 13 are diagrams for explaining a process for moldinga back panel according to a sixth embodiment of the present invention;

[0030]FIG. 14 is a perspective view of the back panel of the sixthembodiment;

[0031]FIG. 15 is a diagram schematically showing an injection moldingmachine according to a seventh embodiment of the present invention;

[0032]FIG. 16 is a diagram schematically showing the urethane injectorof an injection molding machine according to an eighth embodiment of thepresent invention;

[0033]FIG. 17 is a timing chart showing changes in the concentration ofa pigment in the foam molding step of the eighth embodiment; and

[0034]FIG. 18 is a timing chart showing changes in the concentration ofa pigment in another foam molding step.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In the drawings, like numerals are used for like elementsthroughout.

[0036] (First Embodiment)

[0037] The first embodiment of the present invention will be describedbelow with reference to the accompanying drawings.

[0038] As shown in FIG. 4, a steering wheel 1 has an annular gripportion 2, three spoke portions 3, 4 and 5, and a boss plate 6. The gripportion 2 and the spoke portions 3, 4 and 5 are covered with a urethaneresin. The urethane resin portions are formed by reaction injectionmolding. In the reaction injection molding step, the grip portion 2 isset in a metal mold 7 (lower die 8 and upper die 9) shown in FIGS. 1 to3 such that the surface of the steering wheel that faces the driverfaces downward in the mold.

[0039] The metal mold 7 includes a lower die 8 fixed to a frame 11 andan upper die 9 fixed to a cover 12. The frame 11 and the cover 12 form abox 13. Therefore, the metal mold 7 is placed in the inside of the box13. A sealing member 14 is provided in the mating surface of the cover12, which faces the frame 11. The metal mold 7 is moved between an openstate shown in FIG. 1 and a closed state shown in FIG. 2. When the metalmold 7 is closed, the inside of the box 13 is sealed by the sealingmember 14.

[0040] During molding, the frame 11 and the lower die 8 are moved to aclosing position and clamped. A core bar 10 is manufactured by diecasting aluminum, magnesium or alloy thereof. As shown in FIG. 2, a gripcore bar 10 a has a U-shaped cross section.

[0041] A lower recess portion 15 and an upper recess portion 16 areformed in the lower die 8 and the upper die 9, respectively. When themetal mold 7 is closed, a cavity 17 is defined by both recess portions15 and 16. An exhaust hole 20 (having, for example, a cross section of 4mm²) is formed in the upper die 9. The exhaust hole 20 communicates withthe upper recess portion 16 and a hollow portion 21. A lower fixingmember 18 is placed at the center portion of the lower die 8. The lowerfixing member 18 extends in an upward direction. An upper fixing member19 is placed at the center portion of the cover 12. The upper fixingmember 19 extends in a downward direction. As shown in FIG. 2, the corebar 10 is fixed by the lower fixing member 18 and the upper fixingmember 19 during molding.

[0042] An injection nozzle 22 is formed in the side wall of the frame11. A liquid urethane resin material is mixed by an unillustratedurethane injector and injected into the metal mold 7 from the injectionnozzle 22. A urethane material is supplied to the cavity 17 through agate 23. The urethane material contains a polyol component and anisocyanate component.

[0043] An exhaust pipe 31 is installed in the side wall of the frame 11at a position opposite to the injection nozzle 22. The exhaust pipe 31is connected to a vacuum pump 34 by a pipe 32 and a valve 33. The vacuumpump 34 reduces the pressure in the box 13.

[0044] A process for molding the steering wheel 1 according to the firstembodiment will be described below with reference to FIGS. 1 to 3.

[0045] To facilitate the removal of molded products, a parting agent isapplied to the wall of the cavity 17 of the metal mold 7 when the mold 7is opened. The parting agent prevents the molded product from stickingto the metal mold 7. The parting agent contains wax or silicone oil.

[0046] Thereafter, the metal mold 7 is kept horizontal so that the gripportion 2 is positioned on a horizontal plane and a liquid coating M(150 gram in the first embodiment) is injected into the lower recessportion 15. The coating M contains methyl ethyl ketone (MEK) andisopropyl alcohol (IPA), which are solvents, and a urethane resin, whichis a solid filler. MEK, IPA and the urethane resin are contained in thecoating M in amounts of about 85 wt %, about 10 wt % and about 2.5 wt %,respectively. As shown in FIG. 2, the core bar 10 is set in the metalmold 7, and the mold is closed.

[0047] Next, the pressure in the box 13 is reduced by the vacuum pump34. When the pressure in the cavity 17 is reduced, the boiling points ofthe solvents (MEK, IPA) contained in the coating M fall. When thepressure reaches a predetermined level, the coating M boils. Morespecifically, the temperature of the metal mold 7 is maintained at 55°C. When the pressure in the cavity 17 is reduced to 300 Torr or less,the MEK and IPA boil. During the boiling of the MEK and IPA, the coatingM foams and its volume expands. The coating M adheres to the wallsurface of the cavity 17 by the breakage of the foam. Thereafter, thesolvents of the coating M evaporate, and a coating layer of the urethaneresin is formed on the wall surface of the cavity 17. The solvents cleanthe surface of the core bar 10 in the cavity 17. The coating M, whichalso functions as an adhesive, adheres to the surface of the core bar10. The solvents evaporate in about 60 seconds and the evaporatedsolvents are exhausted to the outside of the metal mold 7 through theexhaust hole 20, the hollow portion 21 and the exhaust pipe 31.

[0048] Subsequently, as shown in FIG. 3, the liquid urethane material,which has been mixed by the unillustrated urethane injector, is injectedinto the cavity 17 from the injection nozzle 22 through the gate 23while a predetermined reduced pressure is maintained. The polyolcomponent reacts with the isocyanate component, and the urethane resinfoams and cures.

[0049]FIG. 5 is an enlarged sectional view of the grip portion 2. Sincethe steering wheel 1 is foam molded by injecting the urethane materialinto the cavity 17 under reduced pressure, it has a highly foamed coreportion U2 and a slightly foamed skin layer U3 (refer to Japanese PatentNo. 2518481). This skin layer U3 provides not only a soft feel but alsoa solid feel to the steering wheel 1. A urethane resin coating layer U1having light resistance is formed on the surface of the skin layer U3with a substantially uniform thickness (for example, 10 μm).

[0050] Foam molding using the liquid urethane material is carried out ata lower temperature and a lower pressure in the cavity 17 than theinjection molding of a general thermoplastic resin. Therefore, thecoating layer formed on the wall surface of the cavity 17 is preventedfrom being destroyed by pressure and temperature during molding.Further, since the urethane material is injected into the cavity 17under reduced pressure, the likelihood of a failure to fill the cavity17 with the material is reduced.

[0051] After completion of the molding, the metal mold 7 is opened andthe steering wheel 1 is taken out. Thus, the process of molding thesteering wheel 1 having the grip portion 2 and the spoke portions 3, 4and 5 covered with the urethane layers U1 and U2 is complete.

[0052] By molding with the grip portion 2 facing downward, the coatinglayer U1 on the front side of the steering wheel 1, which is required tohave higher light resistance, has a greater thickness.

[0053] The thickness of the coating layer U1 on the resin surface of thesteering wheel 1 was measured with a color difference meter. The resultis shown in Table 1.

[0054] Table 1 shows the measurement results of the steering wheel ofthe first embodiment and a prior art product coated with the coating Mby means of a spray gun. The urethane resins used for the core portionU2 and the coating layer U1 of the steering wheel 1 have the same color,but a coloring component was removed from the urethane resin of the coreportion U2 to check the state of the coating layer U2 with a colordifference meter. Table 1 shows the measurement results of a pluralityof locations on the grip portion 2. The color of the uppermost portion(front side), where the coating film is thick, is used as a standardcolor, or reference. That is, when the color difference ΔE is zero, thethickness of the coating layer U1 at that position is the same as thatof the uppermost portion. As the color difference ΔE increases, thethickness of the coating layer U1 at that position is less than that ofthe uppermost portion. The locations where measurements were taken arean intermediate position (upper intermediate portion) between theuppermost portion (front side) and the parting line portion (PL portion)of the grip portion 2, the PL portion, an intermediate position (lowerintermediate portion) between the PL portion and the lowermost portion,and the lowermost portion (rear side). TABLE 1 Color differenceMeasurement position First embodiment Prior art Upper intermediateportion ΔE = 0.62 ΔE = 6.63 PL portion ΔE = 0.46  ΔE = 17.89 Lowerintermediate portion ΔE = 1.08 ΔE = 7.91 Lowermost portion ΔE = 0.85 ΔE= 2.80

[0055] As shown in Table 1, the prior art product has a large colordifference ΔE at each position, particularly at the PL portion. Thereason for this is that when the coating solution is applied with aspray gun, the thickness of the coating film is nonuniform.Particularly, the coating thickness at the PL portion, which has asurface substantially perpendicular to the split surface, is less thanthat of the uppermost portion. In contrast, the color difference ΔE isrelatively small at each location, and the coating film has asubstantially uniform thickness in the first embodiment. It is also seenthat a coating film having almost the same thickness as that of theuppermost portion is formed at the PL portion.

[0056] Next, steering wheels molded by changing the amount of eachcomponent of the coating solution were evaluated based on dilutability,coatability and dryability of the coating solution. The results areshown in Table 2 together with the composition of each coating solution.The solid filler in Table 2 is a urethane resin for forming the coatinglayer. When aggregation of the solid filler did not occur at the time ofdilution, the solid filler was marked with O to indicate that it hadhigh dilutability (O represents positive results). On the other hand,when aggregation of the solid filler occurred at the time of dilution,the solid filler was marked with X to indicate that it had lowdilutability (X represents poor results). When the coating solutiondried in less than 60 seconds, it was marked with O to indicate that ithad high dryability. When the coating solution dried in 60 seconds ormore, it was marked with A to indicate that it had low dryability (Δrepresents mixed results). TABLE 2 Amount of each component (gram)Result Solid Dilu- Coat- Dry- fil- Tolu- tabil- abil- abil- Evalu- No.ler IPA MEK ene ity ity ity ation 1 30 130 220 20 ◯ ◯ Δ Δ 2 30 30 220 20X — — X 3 30 530 620 20 ◯ ◯ Δ Δ 4 30 130 620 20 ◯ ◯ ◯ ◯ 5 30 130 1020 20◯ ◯ ◯ ◯ 6 30 130 1420 20 X — — X 7 30 130 1820 20 X — — X

[0057] As shown in Table 2, coating solution No. 1 showed excellentdilutability and coatability but its drying time was long. Therefore,the symbol Δ was used to represent the evaluation. Coating solutionsNos. 2, 6 and 7, which contained a smaller amount of IPA than MEK,showed low dilutability. Therefore, the evaluation was represented withthe symbol X. In coating solutions No. 1, No. 4 and No. 5, the amount ofMEK was increased to a level such that the solid filler did notaggregate. As a result, the drying time of the coating solutionsshortened. Therefore, the evaluation of the coating solutions No. 4 andNo. 5 were represented by the symbol O. When the amounts of MEK and IPAwere increased in coating solution No. 3, the drying time was extended.Therefore, evaluation of the coating solution No. 3 was represented bythe symbol Δ. The coatability of each of the coating solutions Nos. 1,3, 4 and 5, which had excellent dilutability, was satisfactory. However,it was difficult to apply coating solutions Nos. 2, 6 and 7, which hadpoor dilutability.

[0058] Thus, when MEK was added to dilute the coating such thataggregation did not occur, the dryability improved and coatability wasmaintained. Therefore, in the first embodiment, coating solution No. 5,which was prepared by adding MEK in an amount (800 g) 2 times largerthan that (400 g) of coating solution No. 1 to dilute the coating wasused as the resin material for the steering wheel 1.

[0059] When the coating M was applied with a spray gun as in the priorart, the adhesion efficiency to the inside of the cavity 17 was about20%. In contrast to this, in the first embodiment, the adhesionefficiency to the inside of the cavity 17 was about 50 to 70%.

[0060] The first embodiment has the following advantages.

[0061] (1) Since the coating M is applied to the inside of the closedmetal mold 7, the adhesion efficiency is better than when the coating Mis applied with a spray gun. Therefore, the material cost of the coatingM is reduced. The coating M is not applied to portions other than thecavity 17, which prevents the formation of a burr. Therefore, the stepof removing the burr which is required in the prior art is notnecessary. As a result, production cost is reduced. Further, the coatingM is prevented from being scattered, which results in a clean work site,prevents waste and limits environmental damage.

[0062] (2) The coating M is uniformly applied to the wall surface of thecavity 17 due to an increase in the volume of the coating M caused bythe boiling of the solvents and the breakage of foam. As a result, aurethane resin coating layer U1 having excellent light resistance isformed on the surface of the resin portion with a substantially uniformthickness after molding. Therefore, the light resistance issubstantially uniform, which prevents deterioration in the appearanceand performance of the product. Further, the product surface has nocolor difference, which improves the appearance. Moreover, when thesolution of the coating M is poured into the cavity 17, the thickness ofthe film can be adjusted by controlling the amount of the coating M.Thus, a coating film having an appropriate thickness is formed on theparting line portion (PL portion), which has a surface substantiallyperpendicular to the split surface making it difficult to form a thickcoating film in the prior art. Therefore, the light resistance andabrasion resistance is improved in the steering wheel 1. Since thesurface of the metal mold is transferred to the surface of the coatingfilm, a surface design can be easily provided by the metal mold 7. Morespecifically, a smooth surface or uneven surface can be formed on thesteering wheel 1.

[0063] (3) Since the steering wheel 1 is molded such that the surface ofthe steering wheel that faces the driver faces downward, a urethaneresin coating layer U1 is surely formed on the surface of the steeringwheel that faces the driver faces. This improves the light resistance ofthe steering wheel 1.

[0064] (4) Since the surface of the core bar 10 is washed with thesolvents of the coating M, and the urethane resin-based coating M, whichhas excellent adhesion, is applied to the surface of the core bar 10,the core bar 10 and the urethane resin are firmly bonded together.

[0065] (5) Since the reaction injection molding of the urethane materialis carried out while the temperature and pressure of the cavity arelower than that of injection molding with thermoplastic resin, thebreakage of the coating layer on the wall surface of the cavity 17 isprevented. As a result, product yield improves.

[0066] (6) In the first embodiment, coating solution No. 5 (150 g)having composition (MEK=about 85%, IPA=about 10%, urethane resin=2.5%),which is shown in Table 2, was used. Therefore, the coating solution hasexcellent dilutability without aggregation of the solid filler and thecoatability and dryability are satisfactory.

[0067] (7) Since the slightly foamed skin layer U3 is formed around thehighly foamed core portion U2, the abrasion resistance and the textureof the steering wheel 1 are improved. The coating film layer U1, whichis made of a urethane resin having excellent light resistance, is formedon the surface of the resin portion with a substantially uniformthickness. As a result, the light resistance is substantially uniform.Further, the surface of the product has substantially no colordifference. Even when the coating film is worn away by extended use,since the skin layer U3 is formed in the interior portion of thesteering wheel, the appearance and texture of the steering wheel areretained.

[0068] (Second Embodiment)

[0069] The second embodiment of the present invention will be describedbelow with reference to FIG. 6, focusing on its differences from thefirst embodiment.

[0070] The injection molding machine of the second embodiment has acoating injector 40. The dotted lines of FIG. 6 show the cavity 17 andthe gate 23. The coating M is injected into the cavity 17 from thecoating injector 40 through the gate 23. Urethane material, which hasbeen mixed in the urethane injector 41 is injected into the cavity 17through the gate 23. Therefore, the coating solution and the urethanematerial are injected into the cavity 17 through the common gate 23. Inthis injection molding machine, the coating solution is injected intothe cavity 17 while the metal mold 7 is closed.

[0071] The molding step will be described below. A parting agent coatingis first applied to the wall surface of the cavity 17, and the core bar10 is set in the mold metal 7 and clamped. The inside of the cavity 17is depressurized by the vacuum pump 34 to reduce the pressure in thecavity 17 to a predetermined value. The coating M is then injected intothe cavity 17 from the coating injector 40. At this point, the solventsof the coating M boil, which causes the coating M to foam. The coating Mflows toward the exhaust hole 20 in the cavity 17 while the foam breaks.Thus, the coating M is formed on the wall surface of the cavity 17. Aurethane resin coating film is formed on the wall surface of the cavity17 by the evaporation of the solvents.

[0072] After the coating layer is formed on the wall surface of thecavity 17, the urethane material is injected into the cavity 17 from theurethane injector 41. The urethane material reacts and cures in thecavity 17. Thus, the molded steering wheel 1 is produced.

[0073] The second embodiment has the following advantages.

[0074] (1) Since the coating M is injected while the cavity 17 isdepressurized, the resin molding step is performed quickly. Since thecoating M is injected into the closed metal mold 7, the coating M andthe solvents do not leak from the injection molding machine.

[0075] (2) Since the amount of the coating solution injected iscontrolled by the coating injector 40, the thickness of the coatinglayer can be easily adjusted. Therefore, product variations can bereduced.

[0076] (Third Embodiment)

[0077] The third embodiment of the present invention will be describedbelow, focusing on its differences from the first embodiment.

[0078]FIG. 7, FIG. 8 and FIG. 10 are sectional views taken along thespoke portion 4 of an injection molding machine. FIG. 9 is a sectionalview taken along the spoke portions 3 and 5. Four exhaust holes 20 a to20 d are formed in the recess portion 16 of the upper die 9. The exhaustholes 20 a to 20 d communicate with the cavity 17 and the hollow portion21. The exhaust holes 20 a to 20 d are formed at the highest position ofthe cavity 17 in the metal mold 7 as shown in FIG. 8 and FIG. 9.

[0079] The urethane material is liquid and contains a polyol component,an isocyanate component and a foaming component. This urethane materialis injected into the metal mold 7 from the injection nozzle 22 by anunillustrated injection machine.

[0080] The following description is of a process for molding thesteering wheel 1 with reference to FIGS. 7 to 10.

[0081] As shown in FIG. 7, a parting agent is first applied to the wallsurface of the cavity 17 of the opened metal mold 7. Thereafter, thecoating M (170 g) is injected into the recess portion 15 of the lowerdie 8 while the metal mold 7 is horizontal. The coating M containsmethyl ethyl ketone (MEK) and isopropyl alcohol (IPA) as solvents and aurethane resin as a solid filler.

[0082] The core bar 10 is set in the metal mold 7 as shown in FIG. 8 andFIG. 9, and the metal mold 7 is closed and clamped. The vacuum pump 34is driven to depressurize the inside of the box 13. At this point, theair in the cavity 17 is drawn into the hollow portion 21 through theexhaust holes 20 a to 20 d. As a result, the pressure in the cavity 17is uniformly reduced. In response to the reduction in the pressure inthe cavity 17, the boiling points of the solvents of the coating M fall.The coating M flows toward the exhaust holes 20 a to 20 d while itboils. When the pressure in the cavity 17 is reduced to 300 Torr or lessat while the metal mold 7 temperature is 55° C., the solvents boil. Thecoating M is applied to the wall surface of the cavity 17 by the volumeincrease and the breakage of foam during boiling. The solvents containedin the coating M evaporate and the urethane resin of the coating Madheres to the wall surface of the cavity 17. At this point, the coatingM applied to the upper portion of the cavity 17 dries while it flowsdownward. As a result, the coating layer on the bottom side of thecavity 17 is thicker than the coating layer on the ceiling of the cavity17. Further, in the cavity 17, the surface of the core bar 10 is washedwith the solvents, and the coating M, which also functions as anadhesive, adheres to the surface of the core bar 10. The evaporatedsolvents are exhausted to the outside of the apparatus through theexhaust holes 20 a to 20 d by the vacuum pump 34.

[0083] Then, the urethane material, which is a filler material mixed inthe unillustrated injection machine, is injected into the cavity 17 fromthe injection nozzle 22 through the gate 23. The urethane materialreacts and cures in the cavity 17. To describe more specifically, thefoaming component and the isocyanate component react with each other toform CO₂, and the polyol component and the isocyanate component reactwith each other to foam mold the urethane resin.

[0084] Thus, the molding and coating of the urethane resin are carriedout in the grip portion 2 and the spoke portions 3, 4 and 5simultaneously. As a result, the urethane resin coating layer U1, whichis light resistant, is formed on the surface of the urethane resin layerU2. Finally, the metal mold 7 is opened and the steering wheel 1 isremoved.

[0085] Since the resin molding takes place while the steering wheel 1 isupside down (the grip portion 2 faces down) in this embodiment, thethickness of the coating film increases gradually from the rear side tothe front side of the steering wheel 1. The thickness of the coatingfilm on the front side is 10 μm.

[0086] The third embodiment has the following advantages.

[0087] (1) Since the light-resistant urethane resin coating layer U1 isformed on the surface of the foamed urethane resin layer U2,discoloration of the urethane resin layer U2 is prevented. The thickcoating layer is formed on the front side of the steering wheel 1, wherediscoloration is more conspicuous. Further, deterioration in the lightresistance caused by abrasion is prevented without fail. Since a thincoating film is formed on the rear side, the material cost of thecoating M is reduced. Therefore, the cost of preventing the product'sappearance from deteriorating is low.

[0088] (Fourth Embodiment)

[0089] The fourth embodiment of the present invention will be describedbelow, focusing on its differences from the first embodiment.

[0090] In the molding process of this embodiment, the metal mold 7 ishorizontal during a period from when the coating M is injected into thecavity 17 until the cavity 17 is depressurized. This prevents thecoating M from gathering in a predetermined portion of the cavity 17. Asa result, the coating M is uniform on the wall surface of the cavity 17.

[0091] The peel strength of the resin portion to the core bar 10 of thesteering wheel 1 produced by the molding process of this embodiment wasmeasured.

[0092] A steering wheel 1 was prepared by injecting a coating (150 g)into the cavity 17 and reducing the pressure in the cavity 17 to 300Torr (40 kPa) or less to form a coating film on the wall surface of thecavity 17. As a comparative prior art example, a steering wheel wasprepared by forming a coating film on the wall surface of the cavity 17with a spray gun. The results of the peel strengths of the both steeringwheels are shown in Table 3. Table 3 also shows the results obtainedwhen the method of treating the core bar 10 was changed. Morespecifically, the core bar 10 was washed or washed and immersed in anadhesive solution. Table 3 shows the resulting peel strengths neither ofthe above treatments was performed, when the washing treatment wascarried out, and when both the washing treatment and the immersiontreatment were carried out. TABLE 3 peel strength Core bar treatmentFourth embodiment Prior art Untreated 10.8 Nm 1.8 Nm Washing 12.8 Nm 5.6Nm Washing and immersion 14.7 Nm 17.2 Nm 

[0093] As shown in Table 3, the peel strength of the steering wheel 1 ofthis embodiment was 10.8 Nm when the core bar 10 was not treated. Whenonly the washing treatment was carried out, it was 12.8 Nm. When boththe washing treatment and the immersion treatment were carried out, thepeel strength was 14.7 Nm. On the other hand, the peel strength of thesteering wheel of the prior art comparative example was 1.8 Nm when nottreated. When only the washing treatment was carried out, it was 5.6 Nmand when both the washing treatment and the immersion treatment in anadhesive were carried out, it was 17.2 Nm.

[0094] As seen from Table 3, when the film forming method of thisembodiment was employed, even if no surface treatment was performed, thepeel strength was 10 Nm or more and satisfactory adhesion strength wasaccomplished. However, in the comparative example, the peel strength wasunsatisfactory and the surface treatment of the core bar 10 wasindispensable. Therefore, when the forming method of this embodiment isemployed, the washing treatment and the adhesive immersion treatment canbe simplified or omitted.

[0095] The efficiency of the adhesion to the cavity 17 was about 20% inthe prior art comparative example. In contrast, since the coating M wasapplied to the wall surface of the closed cavity 17 in the fourthembodiment, the efficiency of adhesion to the cavity 17 improved toabout 50 to 70%.

[0096] The fourth embodiment has the following advantages.

[0097] (1) Since the surface of the core bar 10 is washed in the cavity17 to remove impurities adhered to the surface, adhesion between thecore bar 10 and the urethane resin improves. Further, in thisembodiment, the urethane resin-based coating M, which has excellentadhesion, is applied to the surface of the washed core bar 10. As aresult, the core bar 10 and the urethane resin are firmly bonded to eachother. Therefore, the step of washing the core bar 10 and the step ofapplying a coat of adhesive on the core bar 10, which are required inthe prior art, can be omitted, which reduces production costs.

[0098] (2) Since the pressure in the cavity 17 is reduced while themetal mold 7 is horizontal, the coating M in the cavity cannot gather atone location and is uniformly formed on the wall surface of the cavity17.

[0099] (Fifth Embodiment)

[0100] The fifth embodiment of the present invention will be describedbelow, focusing on the differences from the first embodiment.

[0101] The urethane material of the fifth embodiment contains a liquidpolyol component (for example, polyether polyol), isocyanate component(for example, diphenylmethane diisocyanate) and water as a foamingagent.

[0102] A description of a process for molding a urethane resin into thesteering wheel 1 of this embodiment follows. Like the first embodiment,the metal mold 7 is first opened and a parting agent is coated on thewall surface of the cavity 17. Thereafter, the liquid coating M (150 g)is injected into the lower recess portion 15 while the metal mold 7 ishorizontal. The core bar 10 is set in the metal mold 7, which is thenclosed and clamped. The vacuum pump 34 is driven to reduce the pressurein the box 13. Then, the solvents of the coating M boil, and theurethane resin of the coating M adheres to the wall surface of thecavity 17. After the coating M is fully dried, the vacuum pump 34 isstopped.

[0103] After the pressure in the cavity 17 reaches normal pressure, theliquid urethane material, which has been mixed by an unillustratedurethane injector, is injected into the cavity 17 from the injectionnozzle 22 through the gate 23 and reacts and cures in the cavity 17 asshown in FIG. 3. To describe more specifically, water and the isocyanatecomponent react with each other to form CO₂, and the polyol componentand the isocyanate component react with each other to foam and mold theurethane resin simultaneously (refer to Japanese Unexamined PatentPublication No. Hei 5-57735). As a result, the molding and coating ofthe urethane resin of the grip portion 2 and the spoke portions 3, 4 and5 of the steering wheel 1 are carried out simultaneously.

[0104] The fifth embodiment has the following advantages.

[0105] (1) The light-resistant urethane resin coating layer U1 is formedon the surface of the urethane resin layer U2, which is molded byfoaming with water to a substantially uniform thickness.

[0106] (Sixth Embodiment)

[0107] In this embodiment, polypropylene (PP) or the like, which hasexcellent moldability and is light and inexpensive, is used as themolding material. Since polypropylene has poor weather resistance, thesurface of a polypropylene resin molded portion is covered with acoating layer having excellent weather resistance. In the sixthembodiment, a back panel 71, which is located between a pair of rightand left tail lamps of an automobile, is molded using the metal mold 7.

[0108] As shown in FIGS. 11 to 13, the metal mold 7 is placed in the box13, which includes the frame 11 and the cover 12. An exhaust hole 20 isformed in the upper recess portion 16 of the upper die 9. The exhausthole 20 communicates with the cavity 17 and the hollow portion 21. Theexhaust hole 20 is also formed at positions corresponding to the cornerportions 1 a of the back panel 71 shown in FIG. 14. Polypropylene isinjected into the cavity 17 from the injection nozzle 22 of anunillustrated injection machine.

[0109] A description a process for molding a resin into the back panel71 follows.

[0110] As shown in FIG. 11, the metal mold 7 is first opened to apply aparting agent coating on the wall surface of the cavity 17 (the recessportion 15 of the lower die 8 and the recess portion 16 of the upper die9). Thereafter, the liquid coating M is injected into the recess portion15 of the lower die 8 while the metal mold 7 is horizontal. The solutionof the coating M in this embodiment contains methyl ethyl ketone (MEK)and isopropyl alcohol (IPA), which are solvents, and a urethane resin,which is a solid filler.

[0111] The frame 11 and the lower die 8 are moved to close the metalmold 7 as shown in FIG. 12. The vacuum pump 34 is then driven to removeair from the box 13. At this point, the air in the cavity 17 is drawninto the hollow portion 21 through the exhaust hole 20, thereby reducingthe pressure in the cavity 17. When the pressure in the cavity 17 isreduced, the boiling points of the solvents (MEK, IPA) of the coating Mfall. The temperature of the metal mold 7 is maintained at normaltemperature (about 20° C.). When the pressure in the cavity 17 reaches70 Torr, the solvents boil. Due to the boiling of the solvents, thecoating M is coated on the wall surface of the cavity 17. Then, thesolvents of the coating M evaporate and the urethane resin adheres tothe wall surface of the cavity 17. The evaporated solvents are exhaustedfrom the exhaust holes 20 through the hollow portion 21 in the box 13and the exhaust pipe 31 by the vacuum pump 34.

[0112] Then, polypropylene, the flowability of which has been improvedby heating in the unillustrated injection machine, is injected into thecavity 17. The polypropylene is cooled and cured in the cavity 17 asshown in FIG. 13. At this point, a urethane resin coating layer U1 thathas excellent weather resistance is formed on the surface of apolypropylene portion P1, which is injection molded and has asubstantially uniform thickness. Finally, the metal mold 7 is opened andthe back panel 71 of FIG. 14 is taken out.

[0113] When the coating M was applied with a spray gun, as in the priorart, the efficiency of adhesion to the cavity 17 was about 20%. Incontrast, when the coating M was formed on the wall surface of theclosed cavity 17, as in this embodiment, the adhesion efficiency to thecavity 17 improved to about 50 to 70%.

[0114] As described above, according to this embodiment, even whenpolypropylene is used, the advantages effects of the first embodimentare likewise achieved.

[0115] (Seventh Embodiment)

[0116] The seventh embodiment of the present invention will be describedbelow with reference to the drawing. This embodiment differs from thesixth embodiment in that a coating injector is provided.

[0117]FIG. 15 is a diagram substantially showing the construction of aninjection molding machine and showing the cavity 17 and the gate 23 bydotted lines. The coating M is injected into the cavity 17 from thecoating injector 40 through the gate 23. Polypropylene, which is heatedby the resin injector 41 and has a low flow resistance, is injected intothe cavity 17 through the gate 23. That is, the coating M and thepolypropylene are injected into the cavity 17 through the common gate23. When the injection molding machine is thus constructed, the coatingM can be injected into the cavity 17 while the metal mold 7 is closed.

[0118] More specifically, after a coating of parting agent is applied tothe wall surface of the cavity 17, the metal mold 7 is closed. Thevacuum pump 34 is then driven to reduce the pressure in the cavity 17,and the coating M is injected into the cavity 17 from the coatinginjector 40 when the pressure in the cavity 17 is reduced to apredetermined value or less. At this point, the solvents of the coatingM boil and the foamed coating M flows toward the exhaust holes 20 in thecavity 17 while the foam breaks. Thus, the coating M is applied to thewall surface of the cavity 17. Then, the solvents of the coating Mevaporate and the urethane resin coating M is formed on the wall surfaceof the cavity 17.

[0119] After the coating layer is thus formed on the wall surface of thecavity 17, the heated polypropylene is injected into the cavity 17. Thepolypropylene cures in the cavity 17 to form the back panel 71.

[0120] According to this embodiment, the advantages effects of the sixthembodiment are likewise achieved.

[0121] (Eighth Embodiment)

[0122] The eighth embodiment of the present invention will be describedbelow with reference to the drawing. In this embodiment, the sameinjection molding machine as in the first embodiment is used. Theinjection nozzle 41 a of the urethane injector 41 is installed in theside wall of the frame 11. The urethane material is mixed in theurethane injector 41 and injected into the cavity 17 from the injectionnozzle 41 a. The urethane material contains a polyol component, anisocyanate component and a coloring component. These three componentsare mixed in the urethane injector 41.

[0123] The urethane injector 41 will be described below with referenceto FIG. 16.

[0124] The urethane injector 41 has a cylinder 42 and a body 43 which isat the end of the cylinder 42 and continuous with the cylinder 42. Theinjection nozzle 41 a is formed at the end of the body 43. The injectionnozzle 41 a is connected to the side wall of the frame 11.

[0125] A through hole 44 is formed in the inside of the body 43. A spool46 is inserted into the through hole 44 so that it can move therein. Thespool 46 is attached to a piston (not shown) which reciprocates in thecylinder 42. The spool 46 is moved by piston between a forward position,shown by broken line, and a rear position, shown by a solid line in FIG.16. A pair of grooves 47 a and 47 b, which extend in the longitudinaldirection of the spool 46, are formed in the outer wall of the spool 46.A mixing chamber 48 is defined by the end surface of the spool 46 andthe wall of the through hole 44.

[0126] Two cylindrical nozzles 49 and 50 are installed in the body 43and are opposed to each other. The polyol component is discharged fromthe first nozzle 49. The isocyanate component is discharged from thesecond nozzle 50. An orifice 51, which is open to the mixing chamber 48or the grooves 47 a and 47 b, is formed in the nozzles 49 and 50. Theopening of the orifice 51 is controlled by a needle 52.

[0127] A reflux hole 53 for the polyol component and a reflux hole 54for the isocyanate component are formed in the body 43 and communicatewith the grooves 47 a and 47 b, respectively. The first nozzle 49 andthe reflux hole 53 are connected to a tank 57 and a pump 58 for thepolyol component by a hose 56. The polyol component flows from the tank57 to the pump 58, nozzle 49, groove 47 a and reflux hole 53 and returnsto the tank 57. The nozzle 50 and the reflux hole 54 are connected to atank 61 and a pump 62 for the isocyanate component by a hose 60. Theisocyanate component flows from the tank 61 to the pump 62, nozzle 50,groove 47 b and reflux hole 54 and returns to the tank 61.

[0128] A discharge passage 64 for discharging the coloring component isformed in the center of the spool 46. The discharge passage 64 connectsthe end surface of the spool 46 to the outer surface of the spool 46. Anintroduction hole 65, which communicates with the discharge passage 64only when the spool 46 moves backward (rightward in FIG. 16), is formedin the body 43. A hose 66 connects the introduction hole 65, a flowcontroller 67, a valve 68 and a tank 69 for the coloring component. Theinside of the tank 69 is always pressurized by an air pressurizing unit70. The opening of the valve 68 is controlled by a timer or the like.The amount of material discharge from the discharge passage 64 iscontrolled by the opening/closing timing of the valve 68 and the flowcontroller 67. A pigment, which serves as the coloring component, isdispersed in the polyol component and stored in the tank 69. Thecoloring material is discharged from the discharge passage 64 throughthe valve 68 and the flow controller 67.

[0129] The coloring material discharged from the discharge passage 64,the polyol component discharged from the nozzle 49 and the isocyanatecomponent discharged from the nozzle 50 are mixed together in the mixingchamber 48. The urethane material is injected into the cavity 17 fromthe injection nozzle 41 a when the spool 46 moves forward.

[0130] A description follows of a process for molding a urethane resininto the steering wheel 1 of this embodiment with reference to FIGS. 1to 3. The urethane resin contained in the coating M has the same coloras the inner urethane resin.

[0131] As shown in FIG. 1, the metal mold 7 is first opened to permit aparting agent to be coated on the wall surface of the cavity 17.Thereafter, the liquid coating M (170 g in this embodiment) is injectedinto the recess portion 15 of the lower die 8 while the metal mold 7 ishorizontal.

[0132] The core bar 10 is then set in the metal mold 7 and the metalmold 7 is closed. The vacuum pump 34 is driven to reduce the pressure inthe box 13 and the cavity 17. When the pressure in the cavity 17 isreduced, the boiling points of the solvents (MEK, IPA) of the coating Mfall. The temperature of the metal mold 7 is maintained at 55° C. Whenthe pressure in the cavity 17 is reduced to 300 Torr or less, thesolvents boil. The coating M is formed on the wall surface of the cavity17 by a volume increase and the breakage of foam during boiling. Whenthe solvents of the coating M evaporate, the coating layer is formed onthe wall surface of the cavity 17. At this point, the surface of thecore bar 10 in the cavity 17 is washed with the solvents of the coatingM and the coating M, which functions as an adhesive, adheres to thesurface of the core bar 10. The pressure in the cavity 17 is reduced to50 Torr and the solvents evaporate in about 60 seconds. The evaporatedsolvents are exhausted from the exhaust hole 20 through the hollowportion 21 in the box 13 and the exhaust pipe 31 by the vacuum pump 34.

[0133] Thereafter, the urethane material, which has been mixed in theurethane injector 41 is injected into the cavity 17 while the reducedpressure is maintained. The urethane material cures in the cavity 17.Consequently, a slightly foamed skin layer U3 and a highly foamed coreportion U2 are formed on the inner side of the urethane resin coatinglayer U1.

[0134] More specifically, the spool 46 is moved backward to dischargethe polyol component from the nozzle 49 and the isocyanate componentfrom the nozzle 50 into the mixing chamber 48. At the same time, thevalve 68 is opened to discharge the coloring material into the mixingchamber 48 from the discharge passage 64 so that it collides with andmixes with the above components. At this point, the concentration of thepigment contained in the urethane material is controlled to 40% of thestandard concentration, for example. When the spool 46 is moved forward,the mixed urethane material is injected into the cavity 17 from theinjection nozzle 41 a. That is, the first urethane material, whichcontains pigment in a concentration that is 40% of the standardconcentration, is injected into the cavity 17 (first injection step).

[0135] Then, gas contained in the urethane material expands suddenlyunder reduced pressure and forms a large number of bubbles. As a result,the urethane material foams in a short period of time and fills thecavity 17 while it flows. Simultaneous with the foaming of the urethanematerial, a reaction (urethane reaction) between the polyol componentand the isocyanate component in the urethane material starts. Duringthis reaction, heat is generated which promotes reaction curing. At thispoint, reaction heat is transmitted to the metal mold 7 in the proximityof the wall surface of the cavity 17, resulting in a temperaturereduction. Therefore, the urethane reaction is slower in the proximityof the wall surface. Also the urethane material near the wall surfacehas a lower viscosity than that in the interior of the urethanematerial. As a result, bubbles near the surface easily break, and aslightly foamed fine skin layer U3, where even very small bubbles do notremain, is formed. Meanwhile, since the viscosity of the interiorportion away from the wall surface of the cavity 17 is raised by theurethane reaction, which proceeds swiftly, bubbles remain in thatportion. As a result, a high foamed core portion U2 is formed. Thus, theskin layer U3 is formed on the surface of the high foamed core portionU2, thereby providing soft and solid feel.

[0136] Subsequently, the amount of the coloring component dischargedinto the mixing chamber 48 from the discharge passage 64 is increased,and a urethane material the pigment concentration of which is set at astandard level (100%), is injected into the cavity 17 from the injectionnozzle 41 a. That is, the second urethane material containing a largeramount of a pigment than the first urethane material is injected (secondinjection step). Consequently, the urethane resin of a portion near thegate is molded. Therefore, even if the urethane resin remaining in thegate portion is cut off later, urethane resin containing a standardconcentration of pigment is exposed, which prevents a defects in theappearance.

[0137]FIG. 17 is a timing chart showing changes in the concentration ofthe pigment in the above molding. That is, as shown in FIG. 17, in thefirst injection step which occurs a period from t1 to t2, the skin layerU3 and the core portion U2 are formed by setting the pigmentconcentration at 40% of the standard level. In the second injectionstep, which occurs in a period from t2 to t3, the portion near the gateis formed with resin having the standard pigment concentration (100%).

[0138] When the steering wheel 1 is thus molded, the concentration ofthe pigment in the skin layer U3 underlying the coating layer is 40%,which is lower than the standard concentration, and the core portion U2has a relatively lower pigment concentration and a lighter color thanthe skin layer U3 because the core portion U2 is foamed. Since the colorof the layered parts of the steering wheel 1 is perceived as a sum ofthe colors of the layers U1, U2, U3, the color of the exposed part,where the gate material was removed and where the pigment concentrationis high, appears to be the same as the remainder of the steering wheel1, the layers of which have lower pigment concentrations.

[0139] A one-dot chain line in FIG. 17 shows a comparative example inwhich the coating M was applied with a spray gun before the foam moldingof the urethane material was carried out. In this case, a burr wasformed on the parting line and a highly foamed core portion was exposedby removing the burr. Therefore, during a period from t1 to t2 when theskin layer and the core portion were formed, the concentration of thepigment had to be increased (for example, to 65%) so that no colordefect would appear where the burr was cut away. However, in the presentinvention, the coating M is only applied to the walls of the cavity 17,and a burr is not formed on the parting line, which makes it possible toreduce the concentration of the pigment.

[0140] The eighth embodiment has the following advantages.

[0141] (1) Although the concentration of the pigment in the skin layerU3 is lower than that of the urethane resin near the gate, the degree ofcoloration of the skin layer U3 is almost the same as that of theurethane resin near the gate because there are almost no bubbles in theskin layer U3. The coating M is not applied to surfaces outside thecavity 17, which prevents burrs. Therefore, the exposure of the coreportion U2 by the removal of a burr is prevented. Further, when thecoating M is applied with a spray gun (mold coating), the coating M isnot uniform. In particular, the coating near the parting line is toothin. However, in this embodiment, a substantially uniform film having adesired thickness formed on the surface of the skin layer U3. Therefore,the urethane resin is covered with the coating film, which makes itpossible to reduce the concentration of the pigment contained in theskin layer U3 and the core portion U2. Even if gate material is cut off,urethane resin having a standard concentration of a pigment is exposed,which prevents a defect in the appearance.

[0142] As described above, the concentration of the pigment contained inthe urethane material can be reduced and the material costs can bereduced without sacrificing the product appearance. The pigmentparticles abrade parts of the urethane injector 41. However, since theconcentration of the pigment can be reduced as described above, theabrasion is reduced. Consequently, the maintenance costs of the urethaneinjector 41 are reduced.

[0143] The above embodiments can be modified as follows.

[0144] In the second embodiment, the coating M may be injected beforedepressurization.

[0145] In the second embodiment, the coating solution may be injectedinto the cavity 17 from a location other than the gate 23.Alternatively, it may be injected into the cavity 17 from a plurality oflocations. In this case, the coating M can be efficiently applied to thewall surface of the cavity 17.

[0146] In the first to sixth embodiments and the eighth embodiment, arubber material and other various kinds of materials may be used as themolding material. Products that can be molded in these embodimentsinclude an instrument panels, console boxes, glow boxes, headrests,armrests, door covers, air spoilers and bumpers. Further, the presentinvention may be applied to the molding of home electric appliances andthe like.

[0147] In the seventh embodiment, ABS resin and other thermoplasticmaterials, that flow resistance of which is improved by heating, may beused. A thermoplastic resin that has absorbed gas at a high pressure maybe injected into the cavity 17 at normal pressure and foam molded. Thiseliminates the need to reduce the molding pressure in the cavity 17 andprevents breakage of a coating layer formed in the cavity 17. Themolding process proposed in Japanese Patent Publication No. Hei 7-119022may be used as an alternative molding process. In this molding process,a molten thermoplastic resin is injected into a resin pool. Then, themetal mold is closed to fill the thermoplastic resin contained in theresin pool into a resin injection space for molding. Also in this case,the pressure is lowered during molding, which prevents the breakage of acoating layer.

[0148] In each of the above embodiments, the components of the coating Mcan be suitably changed. More specifically, other thermosetting resinmay be used in place of a urethane resin. As a solvent for the coatingM, for example, water may be used. From a practical point of view, asolvent having a boiling point of about 160° C. or less at normalpressure may be used.

[0149] In each of the above embodiments, the pressure in the cavity 17may be changed to about 70 Torr when the temperature in the metal mold 7is about room temperature (about 20° C.). The reduced pressure in thecavity 17 may be suitably changed according to the temperature of themetal mold 7 and the types of the solvents used.

[0150] In the first and second embodiments, the coating M may be boiledby heating the metal mold 7 to the boiling points of the solvents underatmospheric pressure without reducing the pressure in the cavity 17.

[0151] In the fourth embodiment, the coating M may be injected into thecavity 17 under normal pressure from the coating injector 40 beforedepressurization instead of after depressurization.

[0152] In the fourth embodiment, a foaming agent that is evaporated byreaction heat between the polyol component and the isocyanate componentmay be used for foam molding in place of CO₂ that is formed by thereaction between the isocyanate component and the foaming component.

[0153] The insert member may be made of a resin or glass.

[0154] In the fourth embodiment, the step of washing the core bar 10 andthe step of applying an adhesive on the core bar 10 may be carried out.In this case, the adhesion strength can be improved. The amount ofadhesive to be applied to the insert member can be reduced according tothe adhesion strength of the coating layer, which reduces materialcosts.

[0155] In the eighth embodiment, since the interior core portion U2 maybe concealed by the skin layer U3 and the coating film (urethane resinlayer U1) according to the shape, color and the like of a moldedproduct, the concentration of pigment in the core portion U2 may bereduced.

[0156] More specifically, during a period from t1 to t10 shown in FIG.18, a first urethane material that has a pigment concentration of 40% isinjected to form the skin layer U2. During a period from t10 to t2, aurethane material that contains no pigment is injected to form theinterior core portion U2. Further, during a period from t2 to t3, asecond urethane material, which has a standard pigment concentration(100%), is injected to deposit urethane resin near the gate. During aperiod from t10 to t2, the injection of urethane material having apigment concentration of 0% may be omitted, and a urethane material(third urethane material) having a lower pigment concentration than atleast the first urethane material may be injected. In the moldingprocess shown in FIG. 18, the injection step during from t1 to t10corresponds to the first injection step, and the injection step duringfrom t2 to t3 corresponds to the second injection step. An injectionstep between the first injection step and the second injection step,that is, an injection step from t10 to t2 corresponds to the thirdinjection step.

[0157] In the eighth embodiment, the pigment concentrations of the skinlayer U3 and the core portion U2 may be suitably changed according tothe shape, color and the like of a molded product. To describe morespecifically, for example, during a period from t1 to t2 when the skinlayer U3 and the core portion U2 are formed, foam molding may be carriedout by gradually reducing the concentration of pigment. When a steeringwheel is molded in the above embodiments, the concentration of thepigment in the urethane material for the surface portion is preferablyreduced to 40 to 80% of the standard level. The concentration of thepigment in the urethane material for the interior portion is preferablyreduced to 30 to 70% of the standard level.

[0158] In the eighth embodiment, a coating injector is providedseparately to inject the coating M into the cavity 17 while the metalmold 7 is closed. Since the coating solution can be injected into thecavity 17 under reduced pressure in this case, the resin molding stepcan be carried out in a short period of time. The coating solution doesnot leak.

[0159] In each of the above embodiments, the molding machine may beequipped with a unit for collecting the coating.

[0160] It should be apparent to those skilled in the art that thepresent invention may be embodied in many other specific forms withoutdeparting from the spirit or scope of the invention. Therefore, thepresent examples and embodiments are to be considered as illustrativeand not restrictive and the invention is not to be limited to thedetails given herein, but may be modified within the scope andequivalence of the appended claims.

What is claimed is:
 1. A process for manufacturing a molded producthaving a coating layer on the surface, comprising: forming a coatinglayer on the wall surface of a cavity while a metal mold is closed; andfilling a filler material in the cavity.
 2. The process according toclaim 1, wherein the forming step includes forming a coating layer onthe wall surface of the cavity by increasing the volume of a coatingsolution in the cavity.
 3. The process according to claim 1 furthercomprising reducing the pressure in the cavity.
 4. The process accordingto claim 1, wherein the foaming step includes supplying a coatingsolution into the cavity and depressurizing the cavity.
 5. The processaccording to claim 1, wherein the forming step includes depressurizingthe cavity and supplying a coating solution into the cavity.
 6. Theproduction process according to claim 1, wherein the filler materialcontains a urethane material that reacts and cures in the cavity.
 7. Theprocess according to claim 2, wherein the coating solution containsmethyl ethyl ketone and isopropyl alcohol as solvents and a urethaneresin.
 8. The process according to claim 1, wherein the forming stepfurther includes the step of heating the metal mold.
 9. A molded productformed by injecting a filler material into the cavity of a metal mold,wherein the filler material is coated with a film having a substantiallyuniform thickness.
 10. The molded product according to claim 9, whereinthe filler material includes a urethane material that reacts and curesin the cavity.
 11. A steering wheel having a first side facing a driverand a second side, which is opposite to the first side, the steeringwheel being coated with a film, the film being thicker on the first sidethan on the second side.
 12. The steering wheel according to claim 11,wherein the thickness of the film gradually increases from the secondside toward the first side.
 13. The steering wheel according to claim 11including a foamed urethane molded portion, wherein the coating filmcovers the foamed urethane portion.
 14. A process for molding a steeringwheel providing a metal mold having a mold cavity, wherein the cavity isformed such that a grip portion of the steering wheel faced downward;comprising: boiling a coating solution, during which a coating layer isformed on the wall surface of the cavity from the coating solution; andsupplying a predetermined filler material into the cavity.
 15. Theprocess according to claim 14, wherein the boiling step includesdepressurizing the cavity.
 16. The process according to claim 15,wherein the depressurizing step includes exhausting gas in the cavitythrough a passage connected to the upper position of the cavity.
 17. Aprocess for manufacturing an insert molded product, comprising: settingan insert member in a metal mold; forming a coating layer on the wallsurface of a cavity in the metal mold while the metal mold is closed;and depositing a filler material into the cavity.
 18. The processaccording to claim 17, wherein the forming step includes boiling acoating solution, wherein a coating layer is formed on the wall surfaceof the cavity in the metal mold from the coating solution during theboiling step.
 19. The process according to claim 17 further comprisingdepressurizing the cavity.
 20. An insert molded product formed bymolding a filler material comprising: an insert member; an intermediatelayer formed from the same material as the coating film and locatedbetween the insert member and the filler material; and a coating filmformed on the surface of the filler material, the coating film having asubstantially uniform thickness.
 21. The insert molded product accordingto claim 20, wherein the filler material contains a urethane material.22. A method of coating a coating on the wall surface of a cavity in ametal mold comprising: closing the metal mold; supplying a solution ofthe coating into the cavity; and depressurizing the cavity.
 23. Themethod according to claim 22, wherein depressurization is carried outuntil the coating solution boils in the depressurizing step.
 24. Amethod of coating a coating on the wall surface of a cavity in a metalmold comprising: closing the metal mold; depressurizing the cavity; andsupplying a coating solution into the cavity during the depressurizingstep.
 25. The method according to claim 24, wherein the step ofdepressurizing the cavity is continued until the coating solution dries.26. A molded product of a urethane resin formed by foam molding usingwater comprising: a core portion molded by foaming a urethane material;and a coating film having a substantially uniform thickness, the filmbeing formed on the surface of the core portion, wherein the surfacecharacteristics of the metal mold is transferred to the coating.
 27. Themolded product according to claim 26, wherein the coating film has athickness of 4 μm or more.
 28. A process for manufacturing a urethaneresin molded product formed by foam molding using water comprising:boiling a coating solution in a cavity in a metal mold while the metalmold is closed, during which time a coating film is formed on the wallsurface of the cavity from the coating solution; and supplying aurethane material into the cavity at normal pressure.
 29. A productmolded with urethane material in a mold cavity comprising: a coreportion made of a highly foamed urethane material; a skin layer formedon the outside of the core portion, the skin layer being made of aurethane material that has less foaming than the core portion; and acoating film formed with a substantially uniform thickness on thesurface of the skin layer, wherein the surface characteristics of thecavity are transferred to the film.
 30. A process for manufacturing afoamed urethane molded product having a surface skin layer comprising:depressurizing a cavity in a metal mold; boiling a coating solution inthe cavity; forming a coating layer on the wall surface of the cavityduring the boiling step; and injecting a urethane material into thecavity under reduced pressure.
 31. The process according to claim 30further comprising supplying a coating solution into the cavity beforethe depressurizing step.
 32. The production process according to claim30 further comprising supplying a coating solution into the cavity afterthe depressurizing step.
 33. A process for manufacturing a resin moldedproduct, wherein molding and coating are performed simultaneously, theprocess comprising: applying a coating solution to the wall surface of acavity in a metal mold; boiling the coating solution in the cavity underreduced pressure to form a coating layer on the wall surface of thecavity; heating a resin material to reduce flow resistance; supplyingthe heated resin material into the cavity; and curing the resin materialin the cavity.
 34. A product molded with resin material, wherein theflow resistance of the resin material can be reduced by heating, whereinthe resin material is coated with a film having a substantially uniformthickness.
 35. A process for manufacturing a urethane molded productcomprising: forming a coating layer on the surface of a cavity of aclosed metal mold; first injecting a first urethane material containinga pigment into the cavity; and second injecting a second urethanematerial that includes a larger amount of a pigment than the firsturethane material.
 36. The process according to claim 35, wherein theforming step is carried out under reduced pressure.
 37. The processaccording to claim 35, wherein the first injecting step is carried outunder reduced pressure.
 38. The process according to claim 35 furthercomprising a third injection step of injecting a third urethane materialcontaining a smaller amount of a pigment than the first urethanematerial after the injection of the first urethane material and beforethe injection of the second urethane material.